Assumptions in Newton's Second Law

  • Thread starter kq6up
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  • #1
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With my understanding of Newton's second -- if I am going to use it to solve a problem, I would need to write ALL velocities in the system with respect to the lab frame (inertial rest frame) -- correct?

Thanks,
Chris
 

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  • #2
A.T.
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With my understanding of Newton's second -- if I am going to use it to solve a problem, I would need to write ALL velocities in the system with respect to the lab frame (inertial rest frame) -- correct?
Velocity doesn't even appear in Newton's second law.
 
  • #3
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It does in the rocket problem. ##\dot{p}=\dot{m}v+m\dot{v}=F_{thrust}##. Also, if you are calculating the the change in momentum over some time interval ##F=m\frac{\Delta v}{\Delta t}##.

Chris
 
  • #4
A.T.
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It does in the rocket problem. ##\dot{p}=\dot{m}v+m\dot{v}=F_{thrust}##. Also, if you are calculating the the change in momentum over some time interval ##F=m\frac{\Delta v}{\Delta t}##.
What, you have there is acceleration and average acceleration, which of course can be expressed in terms of velocity.
 

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